1. Field of the Invention
The present invention relates to a surface treating process for stably vapor-depositing an easily oxidizable vapor-depositing material such as aluminum and zinc onto a work such as a rare earth metal-based permanent magnet, a surface treating apparatus and a vapor-depositing material suitable for carrying out such process, and a rare earth metal-based permanent magnet produced by such process.
2. Description of the Related Art
For a rare earth metal-based permanent magnet having a nature that it is liable to be deteriorated by oxidation, for example, it is a conventional practice to form an aluminum film on the surface of the magnet by vapor deposition to prevent the deterioration of the magnet caused by oxidation. A surface treating apparatus, for example, as shown in FIG. 3, is employed for such a surface treating process.
FIG. 3 shows an apparatus for forming a vapor deposited film of aluminum on the surface of a magnet, more specifically, a rare earth metal-based permanent magnet. A single or a plurality of hearths (a vessel for melting a vapor-depositing material) 2, each of which is a melting/evaporating source for evaporating aluminum 10 as a vapor-depositing material, are disposed on a hearth support base 4 risen on a support table 3 in a lower portion of a treating chamber (a vacuum chamber) 1 connected to an evacuating system which is not shown. Two cage-shaped work retaining members 5 each formed of a net-shaped material are disposed side-by-side for rotation about rotary shafts 6 in an upper portion of the treating chamber 1.
This apparatus is designed, so that rare earth metal-based permanent magnets 30 as works are placed into each of the work retaining members 5, and the aluminum 10 is evaporated from the hearth 2 heated to a predetermined temperature by a heating means (not shown), while rotating the work retaining members 5, thereby forming a vapor deposited film of aluminum on the surface of each of the rare earth metal-based permanent magnets 30 in the work retaining members 5.
However, such surface treating apparatus suffers from (1) a problem that when the vapor deposition process is carried out using such surface treating apparatus under a high partial pressure of oxygen in the treating chamber, the aluminum evaporated from the melting/evaporating source, before reaching the works, is oxidized by oxygen present within the chamber and as a result, an aluminum film having an excellent quality cannot be formed, and (2) a problem that an aluminum oxide film is formed on the surface of molten aluminum within the melting/evaporating source and for this reason, aluminum as the vapor-depositing material is sufficiently not evaporated. If an attempt is made to increase the degree of vacuum for the purpose of reducing the partial pressure of oxygen in order to solve the above problems, it is necessary to carry out an evacuation for a long time. Therefore, if the time taken for the overall processing is supposed to be, for example, 2.5 hours, one hour is required for providing a degree of vacuum equal to or lower than 10xe2x88x924 Pa, resulting in a problem of a poor productivity.
Accordingly, it is an object of the present invention to provide a surface treating process for stably vapor-depositing an easily oxidizable vapor-depositing material such as aluminum onto a work such as a rare earth metal-based permanent magnet without requirement of a long time for providing a high degree of vacuum and without use of a special apparatus, and a surface treating apparatus suitable for carrying out such process and the like.
As a result of zealous studies made to solve the above problems, the present inventors have found that if the vapor-depositing material is evaporated in a state in which zones near the melting/evaporating source and the works within the treating chamber are in such a gas atmosphere that the vapor deposition is controlled by a gas, e.g., by hydrogen, the vapor deposition treatment can be conducted extremely stably without requirement of a long time for providing a high degree of vacuum and without use of a special apparatus.
The present invention has been accomplished based on the above knowledge in view, and to achieve the above object, according to a first aspect and feature of the present invention, there is provided a surface treating process for forming a vapor deposited film from an easily oxidizable vapor-depositing material on the surface of a work, comprising the step of evaporating the vapor-depositing material in a state in which a vapor deposition controlling gas has been supplied to at least zones near a material melting/evaporating source and the work within a treating chamber.
According to a second aspect and feature of the present invention, in addition to the first feature, the wire-shaped vapor-depositing material containing the vapor deposition controlling gas is evaporated, while being supplied to the melting/evaporating source, whereby the vapor deposition controlling gas is supplied from the vapor-depositing material.
According to a third aspect and feature of the present invention, in addition to the second feature, the vapor deposition controlling gas is hydrogen.
According to a fourth aspect and feature of the present invention, in addition to the third feature, the evaporation of the vapor-depositing material is carried out under a partial pressure of oxygen equal to or higher than 10xe2x88x923 Pa.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the molar ratio of hydrogen to oxygen in at least a space between the melting/evaporating source and the work within the treating chamber is in a range of 10 to 250.
According to a sixth aspect and feature of the present invention, in addition to the third feature, the vapor-depositing material is an aluminum wire having a content of hydrogen in a range of 0.5 ppm to 11 ppm.
According to a seventh aspect and feature of the present invention, in addition to the first feature, the vapor deposition controlling gas is supplied by introducing it from the outside of the treating chamber.
According to an eighth aspect and feature of the present invention, in addition to the seventh feature, the vapor deposition controlling gas is hydrogen.
According to a ninth aspect and feature of the present invention, in addition to the eighth feature, the evaporation of the vapor-depositing material is carried out under a partial pressure of oxygen equal to or higher than 10xe2x88x923 Pa.
According to a tenth aspect and feature of the present invention, in addition to the ninth feature, the molar ratio of hydrogen to oxygen in at least a space between the melting/evaporating source and the work within the treating chamber is in a range of 10 to 250.
According to an eleventh aspect and feature of the present invention, in addition to the eighth feature, the vapor-depositing material is aluminum having a content of hydrogen equal to or smaller than 0.5 ppm.
According to a twelfth aspect and feature of the present invention, there is provided a surface treating apparatus comprising a treating chamber connected to a evacuating system, a melting/evaporating source for melting and evaporating a wire-shaped vapor-depositing material containing a vapor deposition controlling gas, a member for retaining a work on which the vapor-depositing material is deposited, the melting/evaporating source and the work retaining member being disposed in the treating chamber, and a vapor-depositing material supply means for supplying the wire-shaped vapor-depositing material containing the vapor deposition controlling gas to the melting/evaporating source.
According to a thirteenth aspect and feature of the present invention, in addition to the twelfth feature, the vapor-depositing material supply means comprises a feed reel for feeding the wire-shaped vapor-depositing material.
According to a fourteenth aspect and feature of the present invention, in addition to the twelfth feature, the vapor deposition controlling gas is hydrogen.
According to a fifteenth aspect and feature of the present invention, in addition to the thirteenth feature, the molar ratio of the vapor deposition controlling gas to oxygen in at least a space between the melting/evaporating source and the work within the treating chamber can be adjusted by the feed rate of the vapor-depositing material fed from the feed reel.
According to a sixteenth aspect and feature of the present invention, there is provided a vapor-depositing material which is a wire having a content of hydrogen in a range of 0.5 ppm to 11 ppm.
According to a seventeenth aspect and feature of the present invention, there is provided a work having a vapor deposited film formed thereon from at least one metal selected from the group consisting of aluminum, titanium, zinc, tin, lead and bismuth by a surface treating process according to the first feature.
According to an eighteenth aspect and feature of the present invention, in addition to the seventeenth feature, the vapor deposited film contains hydrogen.
According to a nineteenth aspect and feature of the present invention, in addition to the eighteenth feature, the content of hydrogen in the vapor deposited film is in a range of 1 ppm to 20 ppm.
According to a twentieth aspect and feature of the present invention, in addition to the seventeenth feature, the work is a rare earth metal-based permanent magnet.
According to the present invention, by evaporating the easily oxidizable vapor-depositing material in a state in which the vapor deposition controlling gas such as hydrogen has been supplied to at least the zones near the melting/evaporating source and the work within the treating chamber, the vapor deposited film can be formed stably from the vapor-depositing material on the surface of a desired work without requirement of a long time for providing a high degree of vacuum and without use of a special apparatus. If the surface treating process according to the present invention is employed, a corrosion resistance can be provided to a rare earth metal-based permanent magnet extremely liable to be oxidized, without degradation of a high magnetic characteristic of the magnet.